The present invention generally relates to refrigeration compressors. More particularly, the invention relates to a system for providing a scroll compressor with low starting torque.
Scroll compressors may be employed to compress refrigerant gas in cooling systems. In a particular application, a scroll compressor may be used in a distributed cooling system of a commercial aircraft. In that context, the scroll compressor may be required to start compression of refrigerant gas in high temperature conditions. For example, the aircraft may be positioned on the ground at a location with a high ambient temperature (e.g. air temperature of 110° F. or higher). In such a case, aircraft equipment bay temperature may be as high as 160° F. Consequently vapor pressure at an inlet side of an idle compressor may be as high as 200 to 250 psia.
A conventional scroll compressor may require application of high torque during start-up under these circumstances. In order to assure that high starting torque may be available; a conventional aircraft cooling system may be constructed with a high-torque motor for driving the compressor. A driving motor that is sized to provide high starting torque may be larger and heavier than a motor that may be sized only to accommodate steady state operational loads of the compressor. In that regard, the conventional compressor may be considered to need an oversized motor. A high-torque driving motor may also require a high capacity (i.e., oversized) inverter to provide a high level of AC current for the motor during compressor start-up. Oversized motors and inverters may add undesirable weight and cost to an aircraft.
As can be seen, there is a need for an aircraft cooling system in which a scroll compressor may be operated with a motor that may be sized in accordance with the compressor's steady state operational loads. Additionally there is a need for a scroll compressor which may be started with such a motor irrespective of ambient temperature in which the aircraft may be present.